Air and Breathing
Air-purifying respirators are the first choice in personal protection against airborne dust, particles, infections and chemical contaminants. The logic is very simple - you have to breathe in a lot of air, and air spaces tend to large and difficult or impossible to clean - hence if you want to breathe better air, strap an appropriate filter on your face and breathe through it - these personal air filters are called air-purifying respirators or APRs.
There are three basic components to a APR
In industrial environments the use of APRs has become standard practice and very precise regulations apply when health risks are known. In the US the National Institute for Occupational Safety and Health ( NIOSH-USA) has been active in testing and certifying respirators. Our choices involve NIOSH approved components.
The personal use of APRs at home, work, on the street, and in cars is not yet common or fashionable. A good APR filters looks weird at first glance - it certainly is not inconspicuous because it requires two large canisters on either side of the face mask. The mask also has to be supported by a neck strap and two elastic straps that go over the top of you head and mess with your hair. Until more people wear APRs and everyone is used to them, we can safely say that if you strap one on to go to work, or walk the dog, most people will say you are weird!
There are problems, of course. The APR is uncomfortable to wear and more expensive to buy than disposable paper filters. An effective filter increases the work of breathing and limits the duration and extent of physical exertions. The canister filters accumulate chemicals and pathogens you want to avoid; they must must be handled with care, disposed of in a safe manner and changed often.
APR or Stand-alone Air Cleaners?
Everyone has been tempted to buy little boxes with fans and filters to clean the air and far too many have been sold on the wish or hope that some good will come out of the little device. The bad news is that household air filters may be of little or no use even when they contain HEFA filters. The basic problem with these boxes is that volume of air to be cleaned is very large and the box is very small. We often read air cleaner specifications that suggest that this cleaner can clean the air an average bedroom three times in an hour. This is OK if the bedroom is sealed and nobody has to breathe in it. If you are in a sealed room of average size with no air exchange you could use up all the oxygen in an hour. As soon as you open the door or window to exchange air, the volume of air that needs to be cleaned probably exceeds the capacity of the air cleaner. If you are sensitive to cigarette smoke and you are sharing the living room with a smoker, the air filter in the corner is not going to help you very much - opening windows to cross-ventilate the room would be a help .
The solution to all airborne hazards is to remove the contaminated air and replace it with clean air. This is ventilation. A professional air-cleaning installation is always based on the principle that air must enter and leave a room at an adequate flow rate to provide oxygen and to dump contaminants. Air filters are placed in the path of incoming air to clean it and outgoing air is exhausted to the exterior. To avoid adding to outdoor air pollution, different strategies of exhaust scrubbing have been invented. The fume hood over a stove, complete with exhaust fan is a good example exhausting contaminated indoor air, but the problems are transferred to neighbours. Modern buildings have vents to allow contaminated air to exit from bathrooms and kitchens; but often the ventilation of the whole building is left to chance. Heat exchangers are a perfect solution in temperate climates often because they allow more air to be moved throughout the building but in cold climates preserve heat so that that cost of ventilation can be reduced as much as 80%.
Information is available for the correct selection, training, and use of respirators. The correct respirator must be selected for the specific hazard in question. Material safety data sheets (if available) often specify the type of respirator that will protect users from risks. We are grateful to the US CDC and the National Institute for Occupational Safety and Health (NIOSH-USA) for their guidance and information.
There are two basic types of respirators:
Atmosphere-supplying respirators include self-contained breathing apparatus (SCBA) and supplied-air respirators (SAR). OSHA has requirements which specify certain aspects of a respiratory protection standard, and these are mandatory legal minimums for a program to be operated. In addition, NIOSH has established comprehensive requirements for the certification of respiratory protection equipment.
Air-Purifying Respirators (APRS)
An air-purifying respirator depends on ambient air purified through a filtering element before inhalation. Three basic types of APRs are used by emergency personnel:
The major advantage of the APR system is the increased mobility it affords the wearer. However, the respirator can only be used where there is sufficient oxygen (19.5%) since it depends on ambient air to function. In addition, the APR should not be used when substances with poor warning properties are known to be involved. The most commonly used APR depends on cartridges or canisters to purify the air by chemical reaction, filtration, adsorption, or absorption. Cartridges and canisters are designed for specific materials at specific concentrations. To aid the user, manufacturers have color-coded the cartridges/canisters to indicate the chemical or class of chemicals the device is effective against. NIOSH recommends that use of a cartridge not exceed one work shift. However, if "breakthrough" of the contaminant occurs first, then the cartridge or canister must be immediately replaced. After use, cartridges and canisters should be considered contaminated and disposed of accordingly.
Disposable APRs are usually designed for use with particulates, such as asbestos. However, some are approved for use with other contaminants. These respirators are customarily half-masks that cover the face from nose to chin, but do not provide eye protection. Once used, the entire respirator is usually discarded. This type of APR depends on a filter to trap particulates. Filters may also be used in combination with cartridges and canisters to provide an individual with increased protection from particulates. The use of half-mask APRs is not generally recommended by most emergency response organizations.
Atmosphere-supplying respirators consist of two basic types: the self-contained breathing apparatus (SCBA), which contains its own air supply, and the supplied-air respirator (SAR), which depends on an air supply provided through a line linked to a distant ambient air source.
Self-Contained Breathing Apparatus (SCBA)
A SCBA facepiece is connected by a hose to a compressed air source. There are three varieties of SCBAS: closed-circuit, open-circuit, and escape. Open-circuit SCBAS, most often used in emergency response, provide clean air from a cylinder to the wearer, who exhales into the atmosphere. Closed-circuit SCBAS, also known as rebreathers," recycle exhaled gases and contain a small cylinder of oxygen to supplement the exhaled air of the wearer. Escape SCBAs provide air for a limited amount of time and should only be used for emergency escapes from a dangerous situation.
The most common SCBA is the open-circuit, positive-pressure type. In this type, air is supplied to the wearer from a cylinder and supplied to the facepiece under positive pressure. In contrast to the negative-pressure units, a higher air pressure is maintained inside the facepiece than outside. This affords the SCBA wearer the highest level of protection against airborne contaminants since any leakage may force the contaminant out. There is a potential danger, when wearing a negative-pressure type apparatus, that contaminant may enter the face mask if it is not properly sealed. The use of a negative-pressure SCBA is prohibited by OSHA under 29 CFR 1910.120(q)(iv) in incidents where personnel are exposed to hazardous materials. However, one disadvantage of SCBAs is that they are bulky and heavy, and can be used for only the period of time allowed by air in the tank. Personnel must be fit-tested for use of all respirators; A tiny space between the respirator and you could permit exposure to a hazard by allowing contaminated air in. Anyone attempting to wear any type of respirator should be trained and drilled in its proper use. Furthermore, equipment must be inspected and checked for serviceability on a routine basis.
Supplied-Air Respirators (SARS)
Supplied-air respirators differ from SCBAs in that the air is supplied through a line that is connected to a source away from the contaminated area. SARs are available in both positive- and negative-pressure models. However only positive-pressure SARs are recommended for use at hazardous materials incidents. One major advantage the SAR has over the SCBA device is that the SAR allows an individual to work for a longer period. In addition, the SAR is less bulky than the SCBA. However, by necessity, a worker must retrace his steps to stay connected to the SAR, and therefore cannot leave the contaminated work area by a different exit.